It is well known that electrical instruments have very broad use in the electrical measuring art. Because of the large number of measurements which are made in regulating processes and apparatus operated electrically there is need for large numbers of instruments. Because of the large number there is a premium on the smaller size instruments so that the instruments can be grouped to give readily available information to persons using the instruments.
Further, because of the very large number of such instruments which are used and the many purposes and applications in which they are employed, it is desirable that they be made at low cost and yet with high reliability and accuracy in performance.
Instruments of the D'Arsonval type include a moving armature or coil assembly which is mounted for rotation through the field of a permanent magnet assembly. When the armature assembly is energized by means of a current flowing therethrough, the resulting magnetic fields interact to produce a torque which rotates the armature assembly relative to the permanent magnet assembly. An instrument pointer is generally connected to the movable armature assembly to yield a readout with respect to a faceplate or scale mounted behind the pointer as the torque is a function of the current magnitude.
One of the requirements for accuracy in electrical instruments of the D'Arsonval type as provided pursuant to the present invention is that they have small profile and yet be capable of producing reproducible readings from one meter to another. In part this is dependent on having a suspension mechanism for the armature assembly which is of desirably low profile and yet which can be produced with great reliability at low cost and in the desirable small size.
Of particular importance is the structuring of the armature assembly so that it will pivot with reliable low resistance to turning. In this respect the pivot mechanism, that is the means on which the armature assembly turns, must have both a low resistance to turning and also a high reproducibility in such low resistance from one meter to another.
Traditionally in the manufacture of moving coil instruments of the D'Arsonval type by prior art technique a pivot element in the form of a pin is used. The pin is assembled into a receiving opening in the center or axis of a cylindrical holder by means of a press fit. The holder with the pin pressed in place is attached in turn to a pointer support by staking the holder into a hole in the pointer support. This assembly is then mounted to the moving coil by bonding as by cement.
A second pivot and holder is pressed into an anchor which is, in turn, cemented to the opposite end of the moving coil. The parts are precisely located in a fixture, according to this prior art method, while the cement is being heat cured. This prior art process requires numerous precision fixtures so that a continuous process of loading the fixture, heat curing, cooling and unloading can be maintained.
While applicant has no specific knowledge of any specific prior art references to the use of punch and die assembly of pivot pins, it is thought that this general concept may have found application in the art of clock and watch making. However, the preparation of a pivot for an instrument and the pivot and instrument prepared are deemed novel and inventive by the applicant.
The general concept of crimping a pointer support assembly and insulator assembly to an armature is disclosed in U.S. Pat. No. 3,597,686 assigned to the same assignee as this application. However, as is evident from the 3,597,686 patent there is no teaching of combination of the crimped pointer support and insulator assemblies in pivot and jewel type instruments. Those distinctions will be made more evident in the description which follows.